1. Field of the Invention
This invention relates generally, to a method of forming fiber and metal composite structures. In particular, the invention relates to forming composite structures from aluminium oxide fibers and magnesium.
2. Description of the Prior Art
Composite materials are generally well known. There are currently in use many composite materials made of various fibers and resins. Fiberglass and boron filament resin composite structures, for example, are in widespread use.
Efforts have been underway for many years to produce composite structures by combining high strength fibers or filaments in a metal matrix. Such efforts have met with some success. However, forming such parts by the method of casting has been difficult. Problems have been encountered in achieving a good bond between the fiber and metal matrix.
A fiber of polycrystalline aluminium oxide has been found to result in an excellent bond with magnesium and aluminium. This fiber was developed by the DuPont Company and is marketed under DuPont's trademark Fiber FP. Such fibers are generally coated with a fugitive organic binder. Fiber FP has been coated with such a binder, Rhoplex. Rhoplex is a trademark of the DuPont Company.
The coated fibers are laid up into a preform. The preform is then heated and compressed. The preform is then placed in a casting mold where the temperature is again elevated so as to permit the binder to either drain or burn off. The voids thus created are then filled by molten metal.
Fiber FP coated with Rhoplex preforms must be subjected to approximately 3,000 pounds per square inch in the compaction step. This requires complex and expensive tooling. Additionally, Fiber FP coated with Rhoplex is extremely brittle resulting in a high fiber failure rate when laying up curved preforms. Additional fibers are broken during compaction. It is difficult to combine preforms of Fiber FP coated with Rhoplex to form more complex structures, prior to their insertion into the casting mold due to Rhoplex's lack of adhesionary characteristics.